topic Re: DF -g & getnasnapshot differences in Microsoft Virtualization Discussions

DF -g & getnasnapshot differences

PALEXOPOULOS — Thu, 05 Jun 2025 06:23:25 GMT

Hi all,

I am currently in the process of automating some capacity reporting but I have come across a discrepancy I can't work out why,.

When I run a df -g on a volume I can see the snap reserve is close to 4.5TB

/vol/*********/	7700GB	5061GB	2638GB	66% /**********/
/vol/***********/.snapshot	3300GB	4643GB	0GB	141% /vol/*********/.snapshot

When I run the following command in powershell

get-nasnapshot $vol.Name | foreach-object{$VolumeSnapSize += $_.Total }

$snapsize = [Math]::Round(($VolumeSnapSize/(1024*1024*1024)),0)

It gives me at total of 7604GB.

Is this because of dedupe on the snapshots? I am stumped and it really throws my reporting out!

Appreciate any help

Re: DF -g & getnasnapshot differences

ashleycook — Mon, 09 Jul 2012 13:16:42 GMT

Sorry, this probably isn't going be much help but I've tried your code against one of our volumes which has dedupe enabled and the output looks to be correct and consistent with ontap. This was against 8.0.3.

/vol/*******/	5120GB	2882GB	2237GB	56% /vol/*******/
/vol/*******/.snapshot	0GB	985GB	0GB	---% /vol/*******/.snapshot

Powershell output: 985

I've tried setting the snapshot reserve to various amounts to see if that was somehow throwing the output, it didn't make any difference, but then I wasn't really expecting it to.

Have you tried breaking down the output a little and checking the output on a per snapshot basis? Something like:

get-nasnapshot $vol.Name |

foreach-object{

$CurrentSnapSize = [Math]::Round(($_.Total /(1024*1024*1024)),0)

Write-Host $_.Name " " $CurrentSnapSize

$VolumeSnapSize += $_.Total

}

Maybe a more verbose output will give you a pointer as to where it is going wrong.

Re: DF -g & getnasnapshot differences

timothyn — Mon, 09 Jul 2012 14:09:49 GMT

Hi Paul,

You definitely understand the problem correctly. Summing the snapshot sizes won't take into account clones or dedupe, so you are likely to get a bad result.

Fortunately, you can use the "Cumulative" property to get the same output as the df command:

(Get-NaSnapshot myvolume | measure -Maximum Cumulative).Maximum

Or if you like formatted data sizes:

(Get-NaSnapshot myvolume | measure -Maximum Cumulative).Maximum | ConvertTo-FormattedNumber -Type datasize

That should get you within rounding error of the df command.

Cheers!

Re: DF -g & getnasnapshot differences

PALEXOPOULOS — Mon, 09 Jul 2012 22:58:17 GMT

Thanks Eric, unfortunately still getting a completely different number!

ashley cook, I outputted the size of each snapshot which gives me the 7TB:

(0151748487)_prd_std_T3_b28_01_r.26705 13

smvi_Clayton-std-daily-01_novmsnap_20120609222000 219

smvi_Clayton-std-daily-01_novmsnap_20120610222000 223

smvi_Clayton-std-daily-01_novmsnap_20120611222000 476

smvi_Clayton-std-daily-01_novmsnap_20120613222000 256

smvi_Clayton-std-daily-01_novmsnap_20120614222000 296

smvi_Clayton-std-daily-01_novmsnap_20120615222000 491

smvi_Clayton-std-daily-01_novmsnap_20120616222000 394

smvi_Clayton-std-daily-01_novmsnap_20120617222000 249

smvi_Clayton-std-daily-01_novmsnap_20120618222000 275

smvi_Clayton-std-daily-01_novmsnap_20120619222000 234

smvi_Clayton-std-daily-01_novmsnap_20120620222006 337

smvi_Clayton-std-daily-01_novmsnap_20120622222000 403

smvi_Clayton-std-daily-01_novmsnap_20120623222000 224

smvi_Clayton-std-daily-01_novmsnap_20120624222001 226

smvi_Clayton-std-daily-01_novmsnap_20120625222000 343

smvi_Clayton-std-daily-01_novmsnap_20120627222000 258

smvi_Clayton-std-daily-01_novmsnap_20120628222000 256

smvi_Clayton-std-daily-01_novmsnap_20120629222000 365

smvi_Clayton-std-daily-01_novmsnap_20120630222000 265

smvi_Clayton-std-daily-01_novmsnap_20120701222000 136

smvi_Clayton-std-daily-01_novmsnap_20120702222000 143

smvi_Clayton-std-daily-01_novmsnap_20120703222000 137

smvi_Clayton-std-daily-01_novmsnap_20120704222000 139

smvi_Clayton-std-daily-01_novmsnap_20120705222000 151

smvi_Clayton-std-daily-01_novmsnap_20120706222001 242

smvi_Clayton-std-daily-01_novmsnap_20120707222000 153

smvi_Clayton-std-daily-01_novmsnap_20120708222000 139

smvi_Clayton-std-daily-01_novmsnap_recent 84

Re: DF -g & getnasnapshot differences

PALEXOPOULOS — Mon, 09 Jul 2012 23:23:08 GMT

Erick using this line: (Get-NaSnapshot myvolume | measure -Maximum Cumulative).Maximum I get the below:

prd_std_T3_b28_01: 7654244847616

Re: DF -g & getnasnapshot differences

ashleycook — Tue, 10 Jul 2012 09:12:49 GMT

Very odd, I can't think of a reason for this.

What I was going to suggest was check the verbose output against System Manager, so you get a view of each snapshot and the cumulative total. I was hoping that might give you an indication of where the output was differing from ontap.

I don't think dedupe should be skewing the output. Certainly when I ran that code the figures returned reflected the dedupe savings. What version of ontap are you running? Just thinking something in the API may have changed between versions.

Re: DF -g & getnasnapshot differences

PALEXOPOULOS — Tue, 10 Jul 2012 12:24:30 GMT

Hi Ashley, 7.3.6.

It's very weird as System Manager is reporting the 7TB as well...

Data Space:

1.98 TB

Snapshot Copies Space:

7.04 TB

Snapshot Overflow Space:

1.67 TB

Total:

9.02 TB

Kind of throws out my capacity reporting completely...

Re: DF -g & getnasnapshot differences

ashleycook — Tue, 10 Jul 2012 12:32:20 GMT

I'm stumped sorry. Maybe someone else running 7.3.x could take a look at their system to see if the results are consistent with what you are seeing?

I've seen disparity between what ontap and operations manager report previously, this has been where seemingly different calculations were used for the dedupe savings. Nothing quite like this though.

Sorry I can't be of more help.

Re: DF -g & getnasnapshot differences

PALEXOPOULOS — Tue, 10 Jul 2012 12:39:30 GMT

Yep it's got me completely stumped as well... Need to start again with my reporting and have a think how I can get around it.

Re: DF -g & getnasnapshot differences

PALEXOPOULOS — Tue, 10 Jul 2012 23:31:38 GMT

Just to throw another curve ball get-nasnapshotreclaimable (unfortunately this method is too slow if I was to use it across all filers) displays a different snapshot size (more consistent with df -g) than what is displayed in the get-nasnapshot and system manager!!

Very weird!

Re: DF -g & getnasnapshot differences

ashleycook — Wed, 11 Jul 2012 09:13:08 GMT

I see what you mean, I also got a slightly result with get-nasnapshot, it is not out by a lot though.

Here is the code I ran, which also incorporates the suggestion which Eric made earlier.

get-nasnapshot $vol.Name | foreach-object{$VolumeSnapSize += $_.Total }

Write-Host "Snapsize 1:" $VolumeSnapSize " = " ($VolumeSnapSize | ConvertTo-FormattedNumber -Type datasize)

$VolumeSnapSize = (Get-NaSnapshot $vol.Name | measure -Maximum Cumulative).Maximum

Write-Host "Snapsize 2:" $VolumeSnapSize " = " ($VolumeSnapSize | ConvertTo-FormattedNumber -Type datasize)

$VolumeSnapSize = Get-NaSnapshotReclaimable $vol.Name -Snapshots ( Get-NaSnapshot $vol.Name * )

Write-Host "Snapsize 3:" $VolumeSnapSize " = " ($VolumeSnapSize | ConvertTo-FormattedNumber -Type datasize)

The ouptut for me was:

Snapsize 1: 48218980352 = 45 GB

Snapsize 2: 48218980352 = 45 GB

Snapsize 3: 48098308096 = 45 GB

Re: DF -g & getnasnapshot differences

timothyn — Wed, 11 Jul 2012 12:50:55 GMT

If you are getting substantially different usage numbers from df and System Manager, you may be better off raising a NetApp support ticket. This doesn't seem like a PowerShell issue.

Cheers,

Eric

Re: DF -g & getnasnapshot differences

PALEXOPOULOS — Wed, 15 Aug 2012 22:59:26 GMT

The new Toolkit seems to have fixed the error. It is also reporting correctly on system manager now as well!